24 June 2026
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As MCS 020 becomes the sole noise standard under Permitted Development, Shane Cox, Managing Director at Itherme, explains why the change places greater emphasis on system design, not just compliance.
From 28th May 2026, MCS 020 becomes the sole standard for demonstrating compliance under Permitted Development, replacing the long-standing 1m from boundary rule.
On paper, that is a positive move. The previous approach massively limited the homes in which heat pumps could be installed. Whereas a more sophisticated methodology based on predicted acoustic levels should allow for better system design and wider deployment. However, it also raises the stakes.
Under the new framework, if a system fails to meet the required noise limits, it falls outside Permitted Development. That brings with it planning applications, delays, redesigns and, ultimately, additional cost. For installers and designers operating at scale, that risk is not theoretical, it’s operational and financial.
And the consequences go beyond compliance alone. As heat pumps continue to scale across the UK, poor acoustic outcomes have the potential to undermine confidence in the technology itself. A system that meets the standard on paper but generates complaints in practice does little to support long-term adoption.
That is why this change matters more than you might think. It shifts responsibility away from simple rules of thumb and places it firmly with those designing, specifying and installing systems.
Calculation is not the same as performance
One of the risks with any standard is the assumption that compliance equals performance. In reality, acoustic performance is not solved at the point of calculation. MCS 020 provides a methodology: it allows installers and designers to predict likely sound levels based on unit data, distances, barriers and environmental factors. But it is only ever as good as the assumptions that sit behind it.
What happens on site is shaped by a far broader set of decisions. Unit selection, for example, plays a significant role. Two systems with similar output capacities can have very different acoustic profiles, particularly at part load or during defrost cycles. This means that selecting a unit based purely on headline performance or cost can introduce issues that are difficult to mitigate later. Positioning is equally critical: a unit placed close to reflective surfaces, within confined spaces, or directly facing neighbouring properties can behave very differently to one installed in a more open environment. But an often-overlooked consideration, is the broader system.
Flow temperatures, emitter sizing and system balancing all influence how a heat pump operates. A system designed to run at lower flow temperatures, with appropriately sized emitters, will typically operate more efficiently and, as a result, more quietly. Conversely, systems forced to work harder to meet demand due to inappropriately sized emitters can experience higher fan speeds, increased cycling and greater noise output.
These are not marginal considerations, they are central to how a system performs in the real world.
The risk of “compliant but problematic”
The introduction of MCS 020 should, in theory, improve consistency. But there is still a risk that systems are technically compliant, but problematic in practice. And often, that comes back to emitter strategy.
A heat pump may satisfy the required noise calculations at design stage, but if the emitters are undersized or poorly configured, the system itself can still become acoustically problematic once operational. When heat cannot dissipate efficiently into the property, the heat pump is forced to work harder to compensate, in turn, increasing flow rates, ramping up fan activity and cycling more aggressively.
That is where “compliant” systems can quickly become unpopular ones.
This is particularly relevant in retrofit projects, where existing radiators are frequently retained despite being designed for far higher operating temperatures. Once flow temperatures drop into the low-temperature range required for efficient heat pump operation, those emitters can struggle to deliver sufficient output. The response, too often, is to push the heat pump harder rather than to address the underlying system design.
In practice, that can create exactly the kind of issues MCS 020 is attempting to avoid: excessive operational noise, dissatisfied occupants and neighbour complaints.
A system-level approach is no longer optional
What MCS 020 effectively does is formalise something the industry has known for some time: heat pump performance cannot be separated from emitter performance.
Acoustics, efficiency and reliability are all outcomes of system design. That means considering how the entire system behaves together. While unit selection matters, so do emitter sizing, flow temperatures, room-by-room heat loss calculations and the ability of the system to deliver stable heat output without forcing the heat pump into excessive cycling. Because when emitters are correctly designed for low-temperature operation, systems tend to run more consistently and more quietly.
This is where underfloor heating can change the dynamic significantly. Because UFH operates across a much larger surface area, it can dissipate heat more evenly and efficiently at lower flow temperatures. Rather than relying on spikes in temperature, the system is able to maintain stable comfort with reduced operational strain, allowing the heat pump to settle into a steadier operating rhythm instead of continually ramping up and down to satisfy demand. The result is not just improved thermal comfort, but quieter operation too.
We recently assessed a heritage property where the heat pump installation itself was technically sound, yet the system had become unpopular due to noise concerns. After recalculating the emitter surfaces and optimising system flow, sound levels reduced considerably while overall energy performance improved at the same time. Cases like this are relatively common but highlight an important point: a “loud heat pump” is rarely just a product issue. More often, it is the symptom of a system that has not been properly engineered for low temperature operation.
At Itherme, this principle sits at the centre of our underfloor heating approach. Systems such as Gypsumdek 18 are specifically designed to support efficient low-temperature operation while also integrating effectively with acoustic floor build-ups, particularly in retrofit and multistorey environments.
Because noise is usually not an isolated acoustic issue, but a warning sign that the wider system has not been optimised correctly.
Designing for quiet is designing for performance
There is a tendency to treat acoustics as a standalone compliance issue. Yet, in reality, quieter systems are usually better-performing systems.
When emitters are properly sized and systems are designed around low temperature operation from the outset, heat pumps settle into a far more stable operating pattern. Cycling reduces, fan speeds remain lower, and strain on the system decreases.
Too often, the focus remains fixed on the outdoor unit itself. But the way heat is distributed throughout the property is what determines how hard the unit needs to work in day-to-day operation.
And, ultimately, quiet performance is not achieved through noise mitigation alone. It is engineered through stable, balanced system design.
https://itherme.com/
